1. Field of the Invention
The present invention relates generally to air bearing sliders for use in magnetic head assemblies and in particular to air bearing slider geometry.
2. Background of the Invention
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1A and 1B, a magnetic disk data storage systems 10 of the prior art includes a sealed enclosure 12, a disk drive motor 14, a magnetic disk 16, supported for rotation by a drive spindle S1 of motor 14, an actuator 18 and an arm 20 attached to an actuator spindle S2 of actuator 18. A suspension 22 is coupled at one end to the arm 20, and at its other end to a read/write head or transducer 24. The transducer 24 (which will be described in greater detail with reference to FIG. 2A) typically includes an inductive write element with a sensor read element. As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is termed in the art, to xe2x80x9cflyxe2x80x9d above the magnetic disk 16. Alternatively, some transducers, known as xe2x80x9ccontact heads,xe2x80x9d ride on the disk surface. Various magnetic xe2x80x9ctracksxe2x80x9d of information can be written to and/or read from the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in a short arc as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 2 depicts a magnetic read/write head 24 including a substrate 25 above which a read element 26 and a write element 28 are disposed. Edges of the read element 26 and write element 28 also define an air bearing surface ABS, in a plane 29, which can be aligned to face the surface of the magnetic disk 16 (see FIGS. 1A and 1B). The read element 26 includes a first shield 30, an intermediate layer 32, which functions as a second shield, and a read sensor 34 that is located within a dielectric medium 35 between the first shield 30 and the second shield 32. The most common type of read sensor 34 used in the read/write head 24 is the magnetoresistive (AMR or GMR) sensor which is used to detect magnetic field signals from a magnetic medium through changing resistance in the read sensor.
In magnetic disk technologies, it is generally desired to achieve higher data recording densities. In the context of the air bearing slider, one way of achieving increased recording densities is by maintaining a low flying height. Maintaining a low flying height requires that, pitch angle and roll angle be held constant over the whole disk surface.
On the one hand, the read/write head 24 must fly at a sufficient height to avoid frictionally related problems caused by physical contact during data communication between the head 24 and the rapidly rotating disk 16. On the other hand, the head 24 should be made to fly as low as possible to obtain the highest possible recording densities. Accordingly, it is preferred that the slider fly as close as possible to the disk surface without actually contacting the disk surface. A constant flying height is preferably maintained, regardless of variations in tangential velocity of the disk 16 during flying, cross movements of the head 24 during data search operations, and changes in skew angle in the case of rotary type actuators.
FIG. 3A is a schematic perspective view of a conventional tapered flat slider 300. Two rails 302 are formed in parallel at a predetermined height on a surface of a slim hexahedron body 304 to thus form lengthwise extending air bearing surface rails (ABS rails) 305. A tapered or sloped portion 306 is formed at each leading edge portion of the ABS rails 305. In such a structure, air within a very thin boundary layer rotates together with the rotation of the disk due to surface friction. When passing between the rotating disk and the slider, the air is compressed by the sloped portion 306 on the leading edge of the ABS rails 305. This pressure creates a hydrodynamic lifting force at the ramp section which is sustained through the trailing edge of the ABS, thus allowing the slider to fly without contacting the disk surface.
The conventional slider of this type suffers a drawback in that the flying height, pitch angle and roll angle vary considerably according to the skew angle of the rotary type actuator, i.e. according to the radial position of the slider over the disk surface. In addition, rapid movement of the actuator arm 20 can cause variations in slider pitch. With reference to FIG. 3B, in order to overcome these variations in slider pitch and to ensure a stable and low level fly height, prior art ABSs have been provided with a cross rail 308, oriented perpendicular to the direction of airflow and located toward the leading edge of the slider. Such a cross rail serves to create a negative or sub-ambient pressure there behind which forces the slider downward. Ideally the downward pressure from the cross bar balances with the upward forces under the rails and a stable fly height is achieved.
When the time comes to terminate use of the data storage system 10 the head 24 must be stored. One prior method referred to in FIG. 3C is known to those skilled in the art as contact start stop (CSS). With the CSS system, upon powering down the system 10, the head 24 lands upon the disk 16. The disk of this system is provided with a landing zone 310. The surface of the landing zone has small bumps, formed with a laser, which prevent the head from sticking to the surface of the disk. The remainder of the disk provides a data zone 312 on which data can be recorded or read. Since any area consumed by the landing zone detracts from available data zone area, in order to increase the total amount of data which can be stored on the disk 16 it is desirable to reduce or eliminate the landing zone 310 in order to increase the data zone.
With reference to FIG. 3D, one method for eliminating the need for a landing zone 310, is called a load/unload system. A landing ramp 314 is provided on which the suspension arm 22 can rest allowing the head 24 to suspend in mid air during non-use. This method advantageously protects the head 24 and recording medium 16 by eliminating the need to contact the head with the medium. However, this method creates other problems in that during unload of the head 24 from the recording medium 16 the sub-ambient pressure tends to resist unloading of the head.
As the head 24 is lifted from the recording medium 16, the high pressure and sub-ambient pressure under the air bearing surface both decrease. However, prior art air bearing designs exhibit an unequal reduction of the pressures as the head 24 is unloaded. The sub-ambient pressures tend to decrease at a significantly lower rate than the high pressures as the distance between the head 24 and the recording medium 16 increases. This creates a net sub-ambient force during unload. In some cases the sub ambient force can be sufficient to cause plastic deformation of the head suspension 22, permanently damaging the system 10, and can cause dimpling of the recording medium 16. Furthermore, the excessive sub-ambient pressure can cause a spring back effect when the sub-ambient pressure is finally overcome, causing the head 24 to severely impact the recording medium 16 damaging both the recording medium and the head.
Thus there remains a need for an ABS having exceptional flight profile characteristics which also exhibit good load and unload characteristics. Such a head would not experience excessive sub-ambient pressures during unload and would preferably be useable in either CSS or load/unload systems.
The present invention provides an air bearing surface (ABS) for use with a magnetic read/write head. The air bearing surface includes a pair of side rails defining there between a channel. The channel terminates at its back end in a cavity also defined between the side rails, and a pressure pad is provided adjacent the trailing edge of the ABS. The cavity of air bearing surface is set at a predetermined distance from the leading edge of the air bearing, the predetermined distance being greater than found in prior art air bearings. The channel and the cavity location both act to reduce sub-ambient pressure experienced under the air bearing during unload of the read/write head.
A pair of front pads are provided located near the front of each side rail. The pressure pads provide lift and also control the pitch of the ABS. In addition, a pair of central pads provided on the side rails midway between the front and rear ends, provide additional lift and help to control pitch and roll of the ABS. The side rails terminate in a pair of rear pads, one on each side rail, which are separated from the central pads by a gap. The rear pads, like the central pads, help to control pitch and roll, to provide a stable flight profile, and the gap allows air to flow there through which facilitates stable flight when the head is flying at a skewed angle.
The trailing edge pad is the location of highest pressure under the air bearing and provides most of the lift. The trailing edge pad includes a step which helps to increase the pressure thereunder. The step can terminate at its trailing edge in either an abrupt edge or a smooth ramp.
An alternate embodiment of the ABS has the front and central pads connected by a bridge. Such a bridge is useful in circumstances where increased pitch is desired. In yet another embodiment, the depth of the cavity can be increased in order to provide additional sub-ambient pressure when necessitated by design parameters such as a need for a lower flying height.